This invention relates to a rotary head drum apparatus and a magnetic recording and playback apparatus, and more particularly to a rotary head drum apparatus and a magnetic recording and playback apparatus wherein a head provided on a rotary head is used to write and/or play back a signal onto and/or from a tape-type recording medium.
In a magnetic recording and playback apparatus of the helical scan type such as a video tape recorder (VTR) wherein a magnetic head contacts with a magnetic tape to effect magnetic recording of the helical scan type onto the magnetic tape, transfer of a signal must be performed between the rotating magnetic head and a circuit on the stationary side. Therefore, as disclosed, for example, in Japanese Patent Laid-Open No. Hei 5-274603, a cylindrical rotary transformer is used, and a stator of the rotary transformer is mounted on an outer circumferential face of a center boss of a stationary drum while a rotor of the rotary transformer is mounted on an inner circumference side of the rotary drum and besides the rotor and the magnetic head are connected to each other by a lead.
However, if it is tried to perform transfer of both of a recording signal and a playback signal at the same time using such a single rotary transformer as disclosed in Japanese Patent Laid-Open No. Hei 5-274603 mentioned above, the recording signal and the playback signal become likely to suffer from deterioration in characteristic by interference, crosstalk or the like on the rotary transformer. This problem is serious particularly where the drum is small in size and besides the video tape recorder is of the multi-channel type wherein many channels are involved. Therefore, a writing rotary transformer and a playback rotary transformer are provided separately from each other so that a writing signal and a playback signal may be transferred separately from each other.
FIG. 3 shows an example of a conventional head drum apparatus which includes a playback rotary transformer and a write rotary transformer provided separately from each other. Referring to FIG. 3, the head drum apparatus shown includes an upper side rotary drum 1, a lower side stationary drum 2, and a motor 3 provided below the stationary drum 2. A magnetic head 4 is mounted on the rotary drum 1 such that it is exposed to the outer circumference of the rotary drum 1.
A playback rotary transformer 6 is disposed above the rotary drum 1. The playback rotary transformer 6 includes a rotor 7 and a stator 8. The rotor 7 is mounted at an upper portion of the rotary drum 1 through a mounting plate 9. Meanwhile, the stator 8 is secured to and supported on a mounting bracket 12 through a mounting plate 10 and an arm 11.
A writing rotary transformer 14 is provided on the inner side of the stationary drum 2. The writing rotary transformer 14 includes a rotor 15 and a stator 16. The rotor 15 is supported on a flange 18 fitted on a rotary shaft 17. Meanwhile, the stator 16 is secured directly to an upper face of a bottom portion of the stationary drum 2.
The rotary shaft 17 is supported for rotation on the stationary drum 2 by a pair of upper and lower bearings 21 and 22. The rotary shaft 17 serves also as a rotary shaft of the motor 3, and a rotor boss 23 of the motor 3 is secured to an end portion of the rotary shaft 17. A rotor yoke 24 is securely mounted on the rotor boss 23, and a ring-shaped magnet 25 is securely mounted on an upper face of the rotor yoke 24.
The magnet 25 of the motor 3 is opposed to a coil 26 with an air gap left therebetween. The coil 26 is mounted on a printed circuit board 27. A shield plate 28 is disposed above the printed circuit board 27, and an outer peripheral wall of the motor 3 is formed from a casing 29 secured to a lower face of the stationary drum 2.
In the head drum apparatus having such a configuration as described above, when the coil 26 on the printed circuit board 27 of the motor 3 is energized, then the magnet 25 mounted on the rotor yoke 24 is acted upon by a force in its rotational direction thereby to rotate the motor 3. The rotation of the motor 3 is transmitted to the rotary drum 1 securely mounted on the rotary shaft 17 so that the rotary drum 1 is rotated. Consequently, the magnetic head 4 mounted on the rotary drum 1 is rotated. A magnetic tape wrapped around and extending between outer circumferential portions of the rotary drum 1 and the stationary drum 2 is opposed to and contacts with the magnetic head 4.
In writing operation, a signal is transmitted from the circuit on the stationary side to the magnetic head 4 on the rotary drum 1 through the stator 16 and the rotor 15 of the writing rotary transformer 14. The signal is written on the magnetic tape. In contrast, in playback operation, a signal of the magnetic tape is read out by the magnetic head 4 and transmitted to the circuit of the stationary side through the rotor 7 and the stator 8 of the playback rotary transformer 6.
In the rotary head apparatus, a favorable characteristic is obtained by providing the playback rotary transformer 6 and the writing rotary transformer 14 in such a manner as shown in FIG. 3 and disposing them in a spaced relationship from each other by a distance as great as possible. Therefore, the rotary transformer 14 is accommodated in the inside of the stationary drum 2, and the playback rotary transformer 6 is disposed above the rotary drum 1.
With the arrangement just described, however, the stator 8 of the playback rotary transformer 6 disposed above the upper side rotary drum 1 must be secured to the rotary drum 1 using such separate structural parts as the mounting plate 10, arm 11, mounting bracket 12. Such a complicated structure as described above is unfavorable in terms of the facility in assembly and the accuracy in assembly and in terms of the cost. Further, the structure makes rework such as exchange of the magnetic head 4 or the like difficult. Particularly where the rotary head drum apparatus is designed for multi-channels and includes many heads, the possibility that a trouble may occur is high. Further, since the playback rotary transformer 6 which has a considerable weight is provided above the rotary drum 1, the rotary head drum apparatus is disadvantageous in dynamic balance and is not suitable for high speed rotation.
It is an object of the present invention to provide a rotary head drum apparatus and a magnetic recording and playback apparatus which are improved in facility in assembly and accuracy in assembly, facilitate rework of a head and the like and assure improved dynamic stability while eliminating the structure wherein one of a writing rotary transformer and a playback rotary transformer is mounted on the upper portion of the rotary drum with a mounting plate, an arm, a mounting bracket and the like.
In order to attain the object described above, according to an aspect of the present invention, there is provided a magnetic recording and playback apparatus and a rotary head drum apparatus, comprising a rotary drum having a head thereon, a stationary drum disposed coaxially with the rotary drum and having, on an outer circumferential face thereof, a guide face for a tape-type recording medium which is opposed to and contacts with the head, and a writing rotary transformer and a playback rotary transformer disposed in a neighboring relationship with each other in an axial direction with a shield plate interposed therebetween and accommodated in the stationary drum.
With the rotary head drum apparatus, upon replacement of the head, the writing rotary transformer and the playback rotary transformer need not be disassembled. Consequently, the rework facility upon replacement of the head is improved. Besides, otherwise possible crosstalk of a writing signal and a playback signal between the two rotary transformers is prevented by the shield plate, and external interference noise is prevented by the stationary drum. Further, since both of the writing rotary transformer and the playback rotary transformer each having large weight can be disposed in a concentrated manner in the stationary drum, the imbalance which may occur is little, and this facilitates balance adjustment upon assembly. Further, with the structure described, the gyro moment when the rotary transformers suffer from a disturbance during operation is small, and the stability upon high speed rotation is improved.
The rotary head drum apparatus may further comprise one of a writing circuit board and a playback circuit board disposed on an end face of the stationary drum. In this instance, the rotary head drum apparatus may further comprise a motor provided adjacent the end face of the stationary drum and having an output power shaft which serves also as a rotationally supporting shaft for the rotary drum, and a fan blade provided on an outer circumference side of a rotor of the motor for cooling the writing circuit board or playback circuit board disposed on the end face of the stationary drum. Alternatively, the rotary head drum apparatus may further comprise the other one of a writing circuit board and a playback circuit board disposed on an end portion of the rotary drum.
According to another aspect of the present invention, there is provided a magnetic recording and playback apparatus and a rotary head drum apparatus, comprising a rotary drum having a head thereon, a stationary drum disposed coaxially with the rotary drum and having, on an outer circumferential face thereof, a guide face for a tape-type recording medium which is opposed to and contacts with the head, a writing rotary transformer and a playback rotary transformer formed from flat disk-type rotary transformers independent of each other and disposed coaxially in a neighboring relationship with each other, and a shield plate interposed between the writing rotary transformer and the playback transformer.
With the rotary head drum apparatus, a writing signal is transferred by the flat disk-type writing rotary transformer, and a playback signal is transferred by the flat disk-type rotary transformer different from the flat disk-type writing rotary transformer. Besides, crosstalk between the two rotary transformers is prevented by the shield plate. Accordingly, an apparatus for transferring signals can be incorporated compactly using a pair of flat disk-type rotary transformers disposed coaxially in a neighboring relationship with each other.
According to a further aspect of the present invention, there is provided a magnetic recording and playback apparatus and a rotary head drum apparatus, comprising a rotary drum having a head thereon, a stationary drum disposed coaxially with the rotary drum and having, on an outer circumferential face thereof, a guide face for a tape-type recording medium which is opposed to and contacts with the head, and a writing rotary transformer and a playback rotary transformer one of which is formed from a flat disk-type rotary transformer and disposed on a bottom portion of the stationary drum and the other of which is formed from a cylindrical rotary transformer and disposed on an outer circumferential portion of a center boss of the stationary drum.
With the rotary head drum apparatus, a writing signal and a playback signal can be transferred separately from each other using a combination of a flat disk-type rotary transformer and a cylindrical rotary transformer. Besides, by disposing the two rotary transformers in the rotary drum, mechanisms for transferring the two different signals can be disposed separately from each other and compactly in the rotary head drum apparatus.
The rotary head drum apparatus may further comprise a shield plate interposed between an end face of the flat disk-type rotary transformer and an upper face of the cylindrical rotary transformer. The writing rotary transformer may be formed from a flat disk-type rotary transformer, and the playback rotary transformer may be formed from a cylindrical rotary transformer.
According to a preferred form of the present invention, the rotary head drum apparatus of the upper drum rotation type is configured such that flat disk-type rotary transformers for exclusive use for writing and for playback are disposed one on the other with a shield plate interposed therebetween, and besides the two rotary transformers are accommodated in the stationary drum. Since the form just described basically has a conventional structure, such factors that raise the cost such as the difficulty in assembly, additional structural parts and the number of man-hours for adjustment are eliminated, and besides the rework facility in replacement of a magnetic head provided on the rotary drum is improved.
Where a writing circuit board for processing a writing signal is disposed on an end face of the stationary drum just below the writing rotary transformer, the loss of a writing signal can be reduced. Further, where a motor is provided below the writing circuit board for processing a writing signal and fan blades are attached to an outer circumference of a rotor of the motor, the writing circuit board can be cooled with wind blasted by the fan blades thereby to radiate the heat.
With the form described above, since flat disk-type rotary transformers for exclusive use for writing and for playback are disposed one on the other with a shield plate interposed therebetween and besides the two rotary transformers are accommodated in the stationary drum, a rotary head drum apparatus of a structure basically same as the structure of a conventional rotary head drum apparatus can be formed. Therefore, the facility in assembly and the rework facility upon replacement of the head of the upper drum and the like are improved. Further, since the two rotary transformers are disposed in the stationary drum, electric shielding by the stationary drum is achieved, and this structure is advantageous against interference noise. Further, since the two rotary transformers each having large weight can be disposed in a concentrated manner at a place in the stationary drum, the imbalance which may occur is little, and this facilitates balance adjustment upon assembly. Further, the gyro moment when the rotary transformers suffer from a disturbance during operation is small, and the stability particularly upon high speed rotation is improved.
Particularly in such a conventional rotary head structure as described above with reference to FIG. 3 which is of the shaft rotation type and wherein the rotary drum 1 is disposed on the upper side, if the rotary transformer 6 is added above the rotary drum 1, then a securing structure for the stator 8 of the rotary transformer 6 which includes such mechanical parts as the mounting bracket 12 is required. In contrast, according to the present invention, such mechanism parts are not required. Therefore, the rotary head drum apparatus of the present invention is much advantageous in terms of the cost, the facility in assembly, additional adjustment and the like. Further, possible output variation caused by a disturbance such as vibrations from a mechanical deck or an impact is reduced.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.